Method of affixing a dental appliance

ABSTRACT

A method for affixing a dental appliance to teeth characterized by effecting a layer of bonding resin and catalyst on the teeth, effecting a layer of a substantially uniform admixture of only two reactants of a three-reactant system, the two reactants including the bonding resin and one of the other reactants, on the teeth; effecting a second layer of a substantially uniform admixture of a second two reactants of said three reactant system, said second two reactants including the bonding resin and the other of the reactants, on the dental appliance to be affixed to the teeth; positioning the portion of the dental appliance adjacent the teeth with the bonding resin, catalyst, and initiator in situ to effect polymerization and bonding on the surface of each of the teeth. After a predetermined cure time, the remainder of the dental appliance is affixed. Also disclosed are the preferred bonding resins, catalysts and initiators, as well as the preferred viscosity and fillers for obtaining the desired viscosity; and an indirect bonding method.

This patent application is a continuation-in-part application of priorU.S. Ser. No. 083,460, now abandoned, filed Oct. 10, 1979, entitled"METHOD OF AFFIXING A DENTAL APPLIANCE"; and itself acontinuation-in-part application of prior U.S. Ser. No. 883,408, nowU.S. Pat. No. 4,200,980, filed Mar. 6, 1978, entitled "ORTHODONTICFORMULATION AND METHOD", the same inventor in each of the cases.

FIELD OF THE INVENTION

This invention relates to a method of affixing a dental appliance toteeth. More particularly, this invention relates to a method of bondingdirectly to the teeth to facilitate affixing a dental appliance thereto.

DESCRIPTION OF THE PRIOR ART

The prior art has seen a wide variety of orthodontic correctiveprocedures to align mal-occluded teeth. Most of these correctiveprocedures employed a dental appliance in one way or another to correctimproper growth of the teeth. The term "dental appliance" is employed inits broad sense in this application to signify any of the applianceswhether to correct the growth of teeth, bridging of the teeth and thelike. Such dental appliances typically include braces, spacemaintainers, elastics, splints, bridge works of more elaborate type andany other type of device that will be affixed to one or more of theteeth in the mouth with the objective of supporting or affecting theaction or growth of other teeth.

A major orthodontic corrective procedure to align mal-occluded teeth isthe placement of metal bands around individual teeth and thereafteraffixing the remainder of the dental appliance to these metal bands. Themetal bands may have affixed bases or brackets, sometimes referred to asthe appliance, or part thereof. Wires having high-tensile strength arethen attached to the metal bands and the fixed portion of the applianceand then to the remainder of the appliance and teeth to affect propertooth movement through the action of the wire itself or of springs orspurs or elastic bands attached to the appliance. The affixedappliances, or brackets require precise positioning to effect propertooth movement.

Adhesive bonding of the affixed appliances to tooth surfaces is theultimate in this type of orthodontic practice in order to eliminate thetedious band fitting procedure and to greatly reduce the decalcificationof teeth and the gingival damage that all too frequently occurs withbanding. Moreover, bonding with a resin type adhesive facilitatescleaning by the patient with less opportunity for food accumulation andconsequent tooth decay compared to the banding because most of theappliances are at the front surface of the teeth in adhesive bondingwith greater accessibility for cleaning.

Despite the advantages of adhesive bonding, it has not achieveduniversal success because of the inconsistent results from the currentlyavailably bonding orthodontic adhesives and the techniques, or methods,of using them.

Currently available orthodontic bonding adhesives generally use one oftwo techniques for applying orthodontic appliances to the teeth. In eachof the techniques the teeth are prepared by cleaning, acid etching,washing and drying.

In the first technique, the bonding resin co-monomer is not mixed with acatalyst but is applied to a clear, transparent plastic bracket that isprecisely positioned on the dried tooth surface. An ultraviolet light isdirected onto the clear bracket so as to penetrate through to initiatepolymerization of the bonding resin. In this way, the viscosity of theresin co-monomer can be adjusted to optimize wetting and avoid creeping;but the requirement for a clear, light-penetrating material for abracket limits the strength of the bracket. Transparent brackets aregenerally inferior to the stainless steel brackets otherwise employed.Consequently, there are frequent failures due to inadequate structuralstrength to resist the stress of the attachment; for example, force byhigh-tensile strength wire. The ultraviolet light itself, if usedindiscriminately, is known to produce skin cancer, especially on softtissue. Consequently, many orthodontists favor another procedure.

Another procedure comprises admixing the exact proportions of anadhesive formulation consisting of filler, catalyst, co-monomer resinand accelerator, or initiator, on a cold plastic slab, or glass plateand the like. The mixing of the catalyst, accelerator, and co-monomerinitiates polymerization of the co-monomer resin immediately so theorthodontist has limited working time to coat the several bases of thebrackets, or portion of the appliance to be bonded to the teeth, and toprecisely position it on the prepared teeth surfaces. Also, theviscosity of the resin is continuously changing with the degree ofpolymerization. This affects positioning and creep of the brackets, aswell as the ultimate bond strength. Viscosity also varies as theproportions of resin and catalyst are varied, deliberately orcarelessly. For example, if the amount of catalyst in relation to theresin is too large, polymerization is too rapid and the higher viscosityof the resulting resin will cause inadequate wetting of the surfaces ofthe teeth and bracket base. (Good wetting onto clean surfaces is themost important criterion in forming strong bonds). The result is a weakbond at best and ultimate displacement of the appliance from the tooth.On the other hand, if the proportion of catalyst is too small, theresulting mixture prepared by the orthodontist or his assistant has alow viscosity due to slow polymerization. This results in "creeping" ofthe appliance from its optimum placement position on a respective tooth.If attempts are made to reposition a bracket, or portion of anappliance, after "creep", then the bond is weakened and the appliancewill ultimately be displaced from the tooth.

From the foregoing, it can be appreciated, that the prior art has notbeen totally satisfactory in solving the problems. First, a thoroughmixing of exactly the right proportions of the adhesive is a requirementin order to evenly disperse the catalyst. Second, even a properlyproportioned admixture forces the orthodontist to work in a limited timeframe without the luxury of being able to correct for unanticipateddelays or contingencies. Otherwise he must begin anew, with wasting oftime and expensive adhesive.

Ideally, a bonding method would have the following features:

1. The bonding method should avoid the use of ultraviolet light orcarcinogenic agents.

2. The bonding method should allow relative freedom of the dentist to beas precise in placement and as careful in maintaining the bracket, orbase of a dental appliance, in position to avoid creep as he wishes,without having to work within a time constraint.

3. The bonding method should provide a relatively constant viscositythat is optimal for effectively wetting the surfaces of the teeth and ofthe dental appliance that is to be bonded to the teeth; simultaneouslyavoiding creep of the bracket, or portion of the dental appliance to bebonded to the teeth.

4. The bonding method should obviate the necessity for careful admixingof predetermined portions so as to be operable even at moments ofcarelessness by the orthodontist or assistant.

5. In specific embodiment, the bonding method should be operable byeither direct bonding or indirect bonding techniques if the latter aredesired to speed up the affixing of the dental appliance.

6. Moreover, in specific aspects, the bonding method should provide ameans that will facilitate application of only one formulation to theportion of the dental appliance that is to be bonded to the teeth andonly one formulation to the tooth, yet produce a final satisfactory bondthat is easily removed at the appropriate time.

7. The bonding method and composition should facilitate usingcomplementary advantageous method steps; such as, forming shields orsealant layers, over the teeth to minimize decay.

In my co-pending Application Ser. No. 883,408, filed Mar. 6, 1978, andentitled "ORTHODONTIC FORMULATION AND METHOD", I disclosed an improvedmethod and composition for direct bonding of the dental appliances toteeth that obviated many of the disadvantages of the prior art. It wasfound, however, that the method of that invention was needlesslycomplex, as were other related methods, such as disclosed in U.S. Pat.Nos. 3,955,282; 4,010,545; 3,738,005; and 3,250,003.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a bondingmethod for bonding a dental appliance to teeth that has one or more ofthe foregoing feature not heretofore provided by the prior art, whilealleviating the disadvantages of the prior art.

It is another object of this invention to provide a method for bonding adental appliance to teeth that has a plurality of the featuresdelineated hereinbefore as desirable and not heretofore provided by theprior art, simultaneously alleviating the disadvantages of the prior artand simplifying the needlessly complex methods thereof.

These and other objects will become clear from the descriptive matterhereinafter, particularly when taken in conjunction with the appendeddrawings.

In accordance with this invention there is provided a method of affixinga dental appliance to at least one tooth in the mouth comprising foreach such tooth a plurality of steps of:

a. effecting on the surface of the tooth to which the dental applianceis to be bonded a layer of a substantially uniform admixture of only afirst two reactants of a three-reactant system consisting essentially ofthe bonding resin, a catalyst and initiator; the first two reactantsincluding the bonding resin and a first one of the other two reactantsthat will effect polymerization of the bonding resin in the presence ofthe second other reactant, the surface of the tooth having been cleanedand dried so as to effect a good bond;

b. effecting on a base of at least a portion of the dental appliancethat is to be bonded to the tooth, the base having been cleaned anddried so as to effect a good bond, a second layer of a substantiallyuniform admixture of only a second two of the reactants of the reactantsystem, the second two reactants including the bonding resin and thesecond other reactant, the bonding resin being polymerized in thepresence of both the other reactants; namely catalyst and initiator;

c. positioning a portion of the dental appliance adjacent the surface ofthe tooth with the layer of bonding resin, catalyst and initiatordisposed between the base and the tooth so as to obtain polymerizationof the resin and the necessary bonding of the base of the dentalappliance to the teeth;

d. after a predetermined cure time sufficient to obtain curing of thebonding resin, affixing the remainder of the orthodontic appliance.

Specifically, the layer that is placed on the surface of the tooth mayinclude the bonding resin and the catalyst; and the layer that is placedon the base of the portion of the dental appliance, or bracket, mayinclude the bonding resin and the initiator. On the other hand, thelayers can be reversed and the bonding resin and initiator applied tothe tooth and the bonding resin and the catalyst applied to the base ofthe dental appliance. It is imperative that only two of the reactants beemployed in each layer such that there is an adequate time to work withthe unit, yet when all three are brought together you have a completethree reactant system, with or without filler for viscosity control. Itis noteworthy that in this embodiment, the bonding resin is provided ineach of the layers. In order to keep this already lengthy patentapplication from becoming unduly long, the discussion hereinafter willbe given with respect to including a layer of the bonding resin andcatalyst on the tooth and a layer of bonding resin and initiator on thebracket base, although it is to be born in mind that these may bereversed if desired.

In other embodiments, indirect bonding is provided.

In the method of this invention, the bonding resins are selected fromclasses consisting of epoxy resin, per se, or capped withhydrolysis-resistant moieties such as the acrylic or methacrylicmoieties; urethane resin; cyanoacrylate resin; methacrylate resin; vinylester resin; and acrylate resin. The filler that is employed to obtainthe critical viscosity comprises small particles of alumina, calciumfluoride, glass, asbestos, or silica. The particle sizes are fromcolloidal sizes up to 35 microns with no particle size large enough tointerfere with the bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a dental appliance bonded to teeth in themouth.

FIG. 2 is an isometric of a tooth having a bracket bonded thereto inaccordance with FIG. 1.

FIG. 3 is a partial cross sectional view of the base of the bracketbonded to the surface of the tooth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The descriptive matter immediately hereinafter is arranged so as todescribe the materials that have been referred to in respective methodsteps. Accordingly, the first descriptive matter will be clarifying whatis meant by the respective bonding resins and catalysts delineated inthe Summary of the Invention hereinbefore.

The bonding resins that are employed in this invention are those resinsthat will bond in the presence of a catalyst to form a firm,substantially permanent bond that resists hydrolysis, even in thepresence of mouth acids and enzymes in the mouth. The bond that isformed, as well as the catalyst and bonding resin should be nontoxic sothat the patient is not adversely affected during the bonding of thedental appliance onto the teeth or the retention of the appliance in themouth. These types of bonding resins are conventionally available andinclude the epoxy resin, per se, or capped with hydrolysis-resistantmoieties; urethane resin; cyano-acrylate resin; methacrylate resin;vinyl ester resin; and acrylate resin. If desired, the resins that haveends that do not resist hydrolysis by their own chemical nature arecapped with hydrolysis-resistant moieties such as the acrylate moiety ormethacrylate moiety. Both the uncapped resins such as epoxy resins andmethacrylic capped epoxy resins are commercially available, as fromDuPont, Wilmington, Del.; Dow Chemical Company, Midland, Mich.; ShellChemical Co.; Houston, Tex.; or Rohm and Haas Chemical Company, St.Louis, Mo. If desired, the resin like the methacrylate capped epoxyresin may have other monomers such as styrene incorporated into itsformulation in order to block hydrolysis of the ester linkage by sterichindrance. To ensure complete understanding, the following structuralformula is given to amplify the definition of the epoxy resins. Theseresins are defined by the structural formula I. ##STR1##

To eliminate the harmful effects of epoxy curing agents the epoxide endsare reacted with the methacrylic moiety shown in formula II. ##STR2##

The methacrylic groups require harmless curing agents to effectpolymerization.

Ordinarily, it is preferred to employ monomer additions, or diluents, toobtain clearer, less viscous monomer solutions. These diluents includestyrene, methyl methacrylate, hydroxy methyl methacrylate, ethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, various polyethylene glycol methacrylatesindividually, trimethylol propane-trimethacrylate, 1,4-butane glycoldimethacrylate, 1,3-butane glycol dimethacrylate, n-propyl methacrylate,n-butyl methacrylate, penta-erythritol tetra methacrylate, and the like.The preferred resin for bonding is methacrylate capped epoxy dilutedwith styrene constituting 40-55 percent of the final admixture; but itsodor is objectionable. Work is being done to overcome this objection.

Preferably, the bonding resin that is employed with the catalyst in alayer on the teeth will have a low viscosity in the range of 250-5,000centipoises at room temperature.

The value of n in the structural formula I is selected such that themolecular weight will be in the range of 10,000-300,000, although it maybe even higher to obtain the desired viscosity with lesser amount offiller as described hereinafter with respect to the layer on the bracketbases.

The polymerization of these types of bonding resins is ordinarilyeffected by free radical initiation employing suitable initiators, oraccelerators, as well as catalyst.

Typical of the initiators are amines such asN,N-dimethyl-para-toluidine; N,N-dimethylaniline; and cobaltnaphthenate. As is recognized, the cobalt naphthenate is ordinarilyemployed with methyl ethyl ketone peroxide catalyst for the epoxide typeresins. The preferred initiator is N,N-dimethyl-p-toluidine.

The catalyst may comprise any of those that are ordinarily employed forpolymerizing these type of monomers. The preferred catalyst for thisinvention is either benzoyl peroxide of methyl ethyl ketone peroxide.

In accordance with this invention, there is no need to mix a powderedcatalyst with a resin to form an admixture that changes viscosity andconsistency during application. Instead, the layer of bonding resin andinitiator, or accelerator, may be formulated to have the desiredcritical viscosity in the range of 25,000-40,000 centipoises measured to50° C. This viscosity is unchanging, therefore, the work time of theorthodontist is essentially limitless, since there is no substantialpolymerization until the layer of bonding resin and catalyst on thetooth is emplaced contiguous the layer of bonding resin and initiator onthe base of the bracket.

In order to obtain the viscosity as defined hereinbefore it is preferredto add an inert filler, in the form of a particulate solid. Preferably,the particles of solid have a predominant size of smaller than 35microns with no sizes so large as to interfere with proper bondingbetween the appliance and the teeth. The filler is selected from thegroup consisting of alumina, barium fluoride, calcium fluoride, glass,asbestos, and silica. Of these, the colloidal silica such as formed byfumed silica is preferable. Thus the optimum viscosity of the bondingresin liquid can be formulated to allow being emplaced intermediate thetwo layers of catalyst on the appliance and the teeth surfaces that areto be bonded together.

Typically the first layer of the bonding resin and catalyst that isemplaced on the teeth will have a proportion of bonding resin in therange of from 90 percent to 98 percent, the remainder being catalyst.

Typically, the second layer of the bonding resin and the initiator has aconcentration in the range of 0.5-3.0 percent by weight of initiator;the optimum concentration of initiator being about 1.5-2.0 percent byweight based on weight of bonding resin and initiator.

The concentration of the filler in the second layer of bonding resin andinitiator may vary depending upon the type of filler and bonding resinbeing employed. With larger filler of, for example, -325 mesh U.S.Standard Sieve, up to 80 percent by weight of filler may be employed.Ordinarily, with colloidal size filler, the concentration of filler willbe in the range of 4-10 percent by weight of the bonding resin. Theoptimum concentration of the filler would be in the range of 6-7 percentof the preferred filler in the preferred resin to obtain the optimumviscosity of about 25,000-40,000 centipoises measured at 50° C.

The cure time is in the range of about 10 minutes to about 2 hours forthe bonding strength to develop sufficient strength in the presence ofthe catalyst and initiator to take the stress attendant to affixing ofthe remainder of the dental appliance. Ordinarily about 15-20 minutesare allowed before the orthodontist, or dentist, begins to affix theremainder of the dental appliance. In point of fact, the bracket basemay be sufficiently adhered to a tooth in as little as 20 seconds toallow moving on to the next teeth. Expressed otherwise, in as little as20 seconds, the base would be bonded sufficiently to the tooth that thebracket holder can be released and another bracket emplaced contiguous,or adjacent, another tooth with the layers of bonding resin, catalystand initiator therebetween.

Ordinarily, an orthodontic appliance may comprise a series of mountingbrackets that are to be bonded directly to the surfaces of the teeth andthe remainder of the appliances high strength wire, connecting thebrackets in a manner so as to apply torque or forces to the teeth toeffect the desired movement of the teeth. The bases of the brackets arebonded to the teeth by one of two methods preparatory to affixing theremainder of the dental appliance. The first is referred to as directbonding. The second is referred to as indirect bonding and is employedto expedite affixing the dental appliance to the teeth.

In direct bonding, the method of this invention is performedindependently for each tooth involved. A multiplicity of steps isinvolved for each of the surfaces of the teeth to which a particular andrespective bracket is to be bonded. For each tooth to be treated, themethod comprises the steps of:

a. cleaning the surface of the tooth to which the bracket is to beaffixed;

b. acidizing the surface of the tooth to which the bracket is to beaffixed to create an etched surface;

c. water washing the acid-etched surface of the tooth to insure it hasbeen thoroughly cleaned;

d. drying the tooth with clean warm air;

e. applying the first layer of bonding resin and catalyst to thecleaned, etched, dried tooth surface;

f. applying to the cleaned, dried base of the bracket a second layer ofcatalyst and initiator;

g. positioning the bracket base adjacent the surface of the tooth withthe intermediate layer of the bonding resin, catalyst and initiator soas to obtain polymerization of the bonding resin and the necessarybonding of the bracket to the tooth;

h. repeating the above described steps for each of the several teethinvolved;

i. after a predetermined cure time, affixing the remainder of the dentalappliance to the brackets.

The method steps may be understood completely by referring to theaccompanying FIGS. 1-3 in conjunction with the following descriptivematter.

FIG. 1 illustrates a dental appliance 11 applied to the teeth 13 by wayof brackets 15. Each of the bases of the brackets are adhered to thesurface of the respective teeth by durable bond 17, FIG. 2. The bond 17,FIG. 3, is formed by polymerization reaction between the first layer 19of bonding resin and catalyst on the surface of the tooth 13 and asecond layer 21 of catalyst and initiator on the base 23 of the bracket15. At the interface, denoted by dashed line 24, the polymerizationreaction expands rapidly, as shown by the intermediate layer 25.Finally, through molecular diffusion of the bonding resin, catalyst andinitiator in the combined layer, a final bond 17 is formed, presumablyby the mechanism of free-radical polymerization.

The component of low viscosity consisting of bonding resin and catalyst(or initiator substituted for the catalyst) is applied to both thecleaned, dried tooth surface and to the cleaned base of the bracket; thesecond component of high viscosity bonding resin containing theinitiator (or catalyst substituted therefor) and filler is applied ontothe layer already present on the base of the bracket, then the bracketis immediately applied to the layer of the first component on the tooth.

In carrying out the method of the invention, the dentist, theorthodontist, or the assistant first cleans the teeth with a suitablematerial such as a pumice type material in the form of a toothpaste orthe like. Such pumices and pastes are conventionally employed and neednot be described in great detail herein. The pumice type paste is thenwashed from the teeth with water and the teeth dried by warm clean dryair. Next an acid etch is applied to the teeth. Ordinarily phosphoricacid having a concentration in the range of 30-50 percent by weight isdabbed onto the teeth with a cotton pellet or light brush. After about aminute and a half, the teeth are rinsed with water again and dried withwarm clean dry air. Next the cleaned metal brackets are arrayed on anabsorbent towel. Preferably, a bracket is selected to have a curvatureof the base to match the curvature of the surface of the tooth to whichit will be adhered. As indicated hereinbefore, the bases of therespective brackets will have been cleaned of all dirt and grease. Thegrease is particularly detrimental to the effecting of a durable bond bythe resin, since it limits the bonding to the surfaces.

A relatively thin layer of the bonding resin and catalyst is applied tothe surface of the teeth to which the brackets are to be affixed, orbonded. As indicated hereinbefore, the bonding resin applied to theteeth has a lower viscosity in the range of 250-5,000 centipoises atroom temperature. There is very little interaction between the catalystand the bonding resin in the absence of an initiator, or accelerator. Topromote polymerization as rapidly as possible but within the time framepermitted, the bonding resin and catalyst are also applied to the baseof the bracket followed by a second layer of higher viscosity bondingresin, initiator and filler.

The bonding resin having the proper amount of viscosity to prevent"creep" and the initiator are admixed together and are applied to thebases of the brackets so as to form a second layer of substantiallyuniform admixture thereon. Preferably a desired amount of filler isincluded in the second layer to obtain the desired viscosity in thedelineated range.

The respective uniform admixtures of, respectively, the bonding resinand catalyst and, the bonding resin and initiator and filler (ifemployed) may be separate prepared admixtures specifically availablecommercially for bonding the bracket to the teeth. Typical such preparedadmixtures are readily available, as from Advance Dental Corporation,Fort Worth, Tex.

Specifically, the relatively low viscosity solution of the bonding resinand catalyst may be brushed onto the teeth and bracket, or splayed ontothe teeth and bracket with a syringe or the like. The second, moreviscous layer of the bonding resin and the initiator can be emplaced onthe bases of the brackets with a spatula or dispensing device such as asyringe, tube or the like. Thereafter, each bracket is positioned on itstooth in the exact location desired. One advantage of this invention isthat it is unnecessary to hold the bracket firmly in place as requiredheretofore. The close contact effects molecular interdiffusion such thatthere is a mixture of the bonding resins, catalyst and initiator toprovide rapid polymerization and finally bonding. For all practicalpurposes, because of the viscosity of the resin, the bracket will remainin place without creeping as soon as it has been firmly emplaced. Thisis one advantages of this invention--that the orthodontist does not haveto waste time holding a bracket until a conventional adhesive buildssufficient gel strength to hold the bracket in place. The next andsubsequent brackets are then similarly treated and applied to the otherteeth.

During the emplacement of the brackets, a small amount of the bondingresin catalyst and initiator is ordinarily extruded from between thebracket base and the tooth surface around the edge of the bracket. Thiscement, or bonding resin, is preferably folded over and around the edgeof the bracket for better mechanical locking in place.

In accordance with this invention, it has been found that the simpleexpedient of employing only two solutions will effect a durable bondwithin about ten to twenty minutes sufficient to allow attaching theremainder of the dental appliance. The thin layer of resin occupies verylittle space between the bracket and the tooth; and, because of therelatively small mass, there is rapid polymerization, producing strongbonds and consistent results; in contrast to the prior art methods.

The affixing of the remainder of the dental appliance is carried out bywiring with the high strength wires as has been done for many years andneed not be described in great detail herein. Similarly, adjustments aremade as conventional.

In the final step, when the orthodontic appliance is ready to beremoved, the orthodontist may unwire the remainder of the appliance andemploy snub-nosed gripper pliers to shear through the cement formed bythe cured bonding resin. One of the advantages of this invention is thatonly about 5 percent of the bonding resin remains on the teeth; whereaswith a conventional mixture about 50 to 100 percent remains on theteeth. The total effect of this small residue is that much less time hasto be spent polishing off the cement, or cured bonding resin, from theteeth with this invention.

In the indirect bonding of the dental appliance to the teeth, a cast ismade of the mouth of the patient and the brackets are temporarilyaffixed into the desired position onto the cast. A layer of soft plasticsuch as polyethylene is folded over the brackets and vacuum drawn intoplace so as to embed the brackets in the soft plastic. Thereafter, thesoft plastic containing the brackets is folded back and the embeddedbrackets are cleaned of the material used to temporarily affix thebrackets to the cast teeth.

A layer of bonding resin and catalyst is effected on the clean dryteeth, similarly as described hereinbefore. Similarly as describedhereinbefore, a layer of bonding resin and initiator is effected on thebases of brackets. The plastic with the brackets embedded therein isinserted into the patients mouth such that the bracket bases aresuitably emplaced adjacent the surfaces of the teeth to which they willbond. The plastic with the brackets emplaced is left in the patientsmouth for a suitable interval of time to bond the brackets to the teeth.This time will be a short time of from only a few minutes to as much asten to twenty minutes. Thereafter, the plastic is removed to leave thebrackets in place on the teeth in the patients mouth. This technique isemployed for speed in applying the brackets.

After the cure time of ten to twenty minutes, the remainder of thedental appliance can be affixed. Adjustments and finally removal arecarried out as described hereinbefore.

The following examples are given to illustrate in a very specific waythis invention.

EXAMPLE I

In this example the orthodontist first cleaned the teeth with a pumicetype toothpaste and water, and wiped clean only with cotton pellet.Thereafter, the orthodontist etched the teeth with a 37.5% solution ofphosphoric acid. This solution was debbed carefully onto the teeth withcotton pellets. This effected a clean acid etch. After allowing aboutone and a half minutes, the acid was thoroughly rinsed from the teethand the teeth were again dried with dry air.

A first layer was formed on the teeth by brushing thereonto asubstantial uniform admixture of monomer resin and catalyst. Anotherlayer of the same material was brushed onto the base of the bracket. Themonomer resin was methacrylate-capped epoxy resin containing styrene andhaving a viscosity of about 500 centipoises at 77° F. The catalyst wasbenzoyl peroxide.

The bracket bases had applied to them a second layer of bonding resinand the initiator. The bonding resin contained 1.2% by weight initiatorand 6.7% by weight a filler. The initiator was N,N-dimethyl-p-toluidine.The filler was fumed colloidal silica, Cabosil from Cobot Corp.,Billerica, Mass. The resin employed was a methacrylate-capped epoxyresin containing styrene amounting to about 45% of the mixute. Theadmixture had the desired viscosity of about 32,000 centipoises measuredat 50° C. The admixture was applied by spatula to the base of each metalbracket.

Each metal bracket was firmly affixed to each tooth by means oftweezers, applying a firm force against each bracket in the exactposition desired. After placement of the bracket on the tooth, the resinheld the bracket in the position without allowing the bracket to creep.The excess bonding resin that was exuded from between the base of thebracket and the tooth was folded around the edge of the bracket with asmall spatula.

The remaining brackets were applied in the same manner.

Sufficient curing time was allowed; for example about 20 minutes; andthe remainder of the appliance was affixed into place against each ofthe brackets to apply the desired force to affect the movement of theteeth in the desired way.

The orthodontist was thereafter able to make adjustments on theappliances that were applied to pull the teeth into the positiondesired. The teeth may be pushed or pulled with this method by using anexternal appliance.

When ready to be removed, the orthodontist employed snub-nosed gripperpliers and sheared through the cement formed by the cured resin. Onlyabout 5% of the total cement remained in place on the teeth. This cementwas polished from the teeth and no ill effects were observed.

EXAMPLE II

The same procedure and steps were carried out in this example as werecarried out in Example I except that the methacrylate capped epoxy resincontained diluent monomers other than styrene. One reactive diluentmonomer was substituted for styrene in a series of resins with differentreactive diluent monomers. For example reactive diluents used in theseries were methyl methacrylate, hydroxy methyl methacrylate, ethyleneglycol dimethylacrylate, diethylene glycol dimethacrylate, triethyleneglycol dimethylacrylate, various polyethylene glycol methacrylatesindividually, trimethylol propane-trimethacrylate, 1,4-butane glycoldimethacrylate, 1,3-butane glycol dimethacrylate, n-propyl methacrylate,n-butyl methacrylate, penta-erythritol tetramethacrylate, and a fewother methacrylate monomers. Each of these resins was found to provide asatisfactory bonding job.

While the method of this invention has been described hereinbeforedirected primarily to the practice of orthodontia, it should beremembered that it may be employed for adhering directly to the teethother dental appliances or the like. Specifically, such things as metalcrowns, protective sheaths, space maintainers, bridges, peridontalsplints, and other such dental appliances of a similar nature may beadhered directly to the teeth through the use of the respective layersof bonding resin and initiator on the respective tooth and dentalappliance.

Having thus described the invention, it will be understood that suchdescription has been given by way of illustration and example and not byway of limitation, reference for the latter purpose being had to theappended claims.

I claim:
 1. A method of affixing a dental appliance to at least onetooth, comprising the steps of:a. effecting on a predetermined etchedand dried surface of the tooth to which a portion of a dental applianceis to be bonded a first layer of a substantially uniform admixture oftwo reactants of a three-reactant system consisting essentially of abonding resin that is hydrolysis resistant, that is partiallypolymerized and that will polymerize further in the presence of acatalyst and an initiator to bond in the presence of acids and enzymesin the mouth and selected from the class consisting of epoxy resin,urethane resin, methacrylate resin, vinyl ester resin, and acrylateresin; a catalyst that will affect polymerization of said bonding resinand selected from the class consisting of benzoyl peroxide, and methylethyl ketone peroxide; and an initiator selected from the classconsisting of N,N-dimethyl-para-toluidine, N,N-dimethyl aniline, andcobalt naphthenate; said two reactants including said bonding resin andeither one said catalyst or initiator that will affect polymerization ofsaid bonding resin; b. effecting on a cleaned and dried surface of atleast a portion of a dental appliance that is to be bonded to saidtooth, a proper viscosity second layer of a substantially uniformadmixture of two reactants of said three-reactant system, said tworeactants including said bonding resin and the other of said initiatoror said catalyst; and said bonding resin being polymerized by saidsecond other reactant in the presence of said first other reactant; andc. positioning said at least a portion of said dental appliance adjacentsaid surface of said tooth wherein said two layers containing saidbonding resin, catalyst and initiator are brought together to obtainpolymerization of said bonding resin and hence the necessary bonding ofsaid at least a portion of the dental appliance to the surface of thetooth; said proper viscosity being obtained by a filler added to saidsecond layer to obtain the desired viscosity of said resin, to avoidcreep and to obtain the desired wettability of said tooth to said threereactants.
 2. The method of claim 1 wherein said two reactants of saidfirst layer on said tooth comprises said bonding resin and said catalystthat will effect polymerization of the bonding resin in the presence ofsaid initiator; and said second layer comprises said bonding resin andsaid initiator that will effect polymerization of said bonding resin inthe presence of said catalyst.
 3. The method of claim 2 wherein saidproper viscosity of said second layer of said resin and accelerator is aviscosity in the range of 25,000-40,000 centipoises measured at 50° C.temperature.
 4. The method of claim 3 wherein said second layer has anoptimum viscosity of about 32,000 centipoises measured at 50° C.
 5. Themethod of claim 1 wherein said filler is selected from a groupconsisting of alumina, calcium fluoride, barium fluoride, glass,asbestos, and silica; said filler being in the form of particles thatare predominantly in a size up to 35 microns and have no size so largeas to interfere with the bonding of said at least a portion of saiddental appliance to said tooth.
 6. The method of claim 5 wherein saidfiller is colloidal silica.
 7. The method of claim 6 wherein saidcolloidal silica comprises fumed silica and is present in theconcentration in the range of 6-7 percent by weight, inclusive.
 8. Themethod of claim 5 wherein said filler is present in the concentration inthe range of 4-10 percent by weight.
 9. The method of claim 1 whereinsaid bonding resin is selected from the class consisting of partiallypolymerized methacrylate resin and acrylate resin.
 10. The method ofclaim 1 wherein said catalyst is benzoyl peroxide.
 11. The method ofclaim 1 wherein said initiator is selected from the class consisting ofN,N-dimethyl-p-toluidine, N,N-dimethylaniline.
 12. The method of claim11 wherein said initiator is present in the concentration within therange of 0.5-3.0 percent by weight.
 13. The method of claim 1 whereinsaid first layer of said substantially uniform admixture is applied toboth said tooth and said bracket before said proper viscosity secondlayer of said substantially uniform admixture is applied to saidbracket.
 14. The method of claim 1 wherein said dental appliance isaffixed to brackets that are affixed to the respective surfaces of aplurality of teeth and a plurality of respective said brackets areaffixed to each of a plurality of respective said teeth by the stepsof:a. cleaning the surface of the tooth to which said bracket is to beaffixed; b. acidizing the surface of said tooth to which said bracket isto be affixed to create a cleanly etched surface; c. rinsing the acidetched surface of said tooth to insure that it has been water washed andthoroughly cleaned; d. drying said tooth with clean air; e. applying tothe surface of said tooth a layer of said bonding resin and saidcatalyst that will polymerize said resin in the presence of aninitiator; f. cleaning and drying the base of said bracket; g. applyingto the cleaned, dried base of said bracket a proper viscosity layer ofsubstantially uniform admixture of said bonding resin that willpolymerize in the presence of said initiator and said catalyst and saidinitiator that will effect polymerization of said bonding resins in thepresence of said catalyst; h. positioning said bracket adjacent saidsurface of said tooth with the intermediate layers of bonding resincontaining said catalyst and said initiator so as to obtainpolymerization of the bonding resin and the necessary bonding of thebracket to the tooth; and i. after a predetermined cure time, affixingthe remainder of said dental appliance to said brackets.
 15. The methodof claim 14 wherein said layer of bonding resin and catalyst inaccordance with step e, is applied to the cleaned and dried base of saidbracket following step f. and before step g.
 16. A method of affixing adental appliance to teeth; said dental appliance including both bracketsthat are to be affixed to said teeth and the remainder of said dentalappliance, and said brackets are affixed to said teeth by indirectbonding comprising a plurality of steps of:a. making a cast of the teethand mouth of the patient; b. temporarily arranging the brackets on saidcast; c. folding over said brackets a layer of soft plastic andembedding said brackets in said plastic; d. removing said plastic andbrackets and applying to the clean bracket bases a proper viscositylayer of a substantially uniform admixture of two reactants of athree-reactant system consisting essentially of a bonding resin that ishydrolysis resistant, that is partially polymerized and that willpolymerize further in the presence of a catalyst and an initiator tobond in the presence of acids and enzymes in the mouth and selected fromthe class consisting of epoxy resin, urethane resin, methacrylate resin,vinyl ester resin, and acrylate resin; a catalyst that will affectpolymerization of said bonding resin and selected from the classconsisting of benzoyl peroxide, and methyl ethyl ketone peroxide; and aninitiator selected from the class consisting ofN,N-dimethyl-para-toluidine, N,N-dimethyl aniline, and cobaltnaphthenate; said two reactants including said bonding resin and eitherone of said initiator or catalyst that would effect polymerization ofsaid bonding resin; e. applying to the surfaces of said teeth after saidteeth have been cleaned and dried, a substantially uniform admixture oftwo reactants of said three-reactant system; said second two reactantsincluding said bonding resin and the other of said catalyst or initiatorthat would effect polymerization of said bonding resin; f. insertingsaid plastic with said brackets in place and with said resin, catalystand initiator intermediate said bases of said brackets and said teethsuch that said brackets are emplaced adjacent the surface of said teethand polymerization of said bonding resin is effected to adhere saidbrackets on to said teeth, and leaving said plastic in place for aperiod of at least several minutes to twenty minutes; g. removing saidplastic to leave said brackets in place on said teeth with said bracketsbonded directly to said teeth; and h. allowing sufficient time for cureof said bonding resin and thereafter affixing the remainder of saiddental appliance.
 17. The method of claim 16 wherein said first tworeactants comprise said bonding resin and said initiator; and saidsecond two reactants comprise said bonding resin and said catalyst suchthat when the two layers are brought together all three reactants ofsaid three-reactant system are available for effecting polymerization ofsaid bonding resin and bonding of said dental appliance to said teeth.